1. Field of the Invention
This invention relates to furnaces and heating devices. Specifically in this case an object of the invention is to provide complete combustion of the material used as fuel therein, so that no dirty smoke results from the fire.
2. Description of the Prior Art
Furnaces have been built in many forms in the past. A basic form involves an arrangement wherein solid fuel is burned on a grate. Depending on the actual fuel used, and its particulate size or granularity, combustion of fuel resting on a single grate is almost invariably incomplete, resulting in unburned particles, which produce smoke and ash. When the particles or pieces of fuel are reduced to a size smaller than the openings in the grate, they will fall through into an ash pit or fire pit where they will probably smolder or burn even less completely.
In a typical updraft furnace, where the combustion air flows up through the layer of fuel on the grate, the fuel will burn unevenly so that unburned particles of fuel are carried off out the chimney or flue, resulting in incomplete combustion and creating dirty, dark smoke.
Particular forms of furnaces have been devised to attempt to provide more complete and efficient combustion of the fuel, for the purpose primarily of achieving greater heat production by the more efficient use of the fuel, and also in some cases with the additional purpose of reducing smoke.
For example, a U.S. Patent to Roell, issued in 1907 (U.S. Pat. No. 843,105) was entitled Smoke Consuming Heater. In this invention after the fire is burning, air is led through passages around the firepot to heat it (the air) further, and, per the teaching of the patent, increase the heat output and reduce the smoke in the exhaust.
An earlier patent (U.S. Pat. No. 464,425, 1891, to C. R. Burr) involves an improved furnace which is intended to achieve complete combustion of the fuel by the use of dual grates, one above the other, the upper one intended to serve as a fuel feed for the lower. In this design, the grate bars are hollow and diverge from front to rear. Intake air passes partly through the upper grate's hollow bars, and is led down into the space between the grates, to provide a downward draft through the fuel on the lower grate into the ashpit below and to a following combustion chamber. Part of the intake air also passes through the hollow bars of the lower grate and mixes subsequently with the other intake combustion air. Fuel is put on the upper grate, the bars of which diverge from front to rear, providing a greater spacing between the bars at the front than at the rear. During combustion, the fuel on the upper grate must be raked or agitated so that it falls through the grate onto the lower one, supplying it with fuel already burning or pre-heated. In this design, it does not appear that the means chosen will assure that the lower grate is completely covered with fuel, so that unburned gas can pass through the grate and final combustion must occur in the ashpit or its associated chamber. Such combustion is unlikely to be complete enough to prevent the emission of a significant amount of smoke.
Another U.S. Pat. No. 1,954,923, to Eichhorn (1934), describes a furnace which may be operated in either a downdraft or updraft mode. This, however, is a single grate furnace with a shelf below the grate having an opening into an ashpit, so that fuel falling through the grate will be caught on the shelf or fall into the ashpit, in both cases to smolder and burn incompletely, with smoke resulting. While Eichhorn provides for auxiliary air passages to provide pre-heated air for the downdraft mode, the patent states that in the downdraft mode an upper damper should be partially open, permitting accumulated smoke to be drawn off from above the coal bed into a smoke box, from which it apparently exhausts.
In equipment so basic as a furnace, many other designs for both updraft and downdraft operation have been proposed.